The present invention relates to a selective optical resonator and apparatus utilising the same. It is used in optics, particularly in the construction of mono-frequency and/or frequency stabilised lasers.
Numerous selective resonators are known and they are more particularly used in the laser field. They comprise two facing mirrors and between the said mirrors a selective means for giving preference to a particular wavelength. This means can be a prism, a defraction grid, a Fabry and Perot interferometer, etc. Said apparatus can also be considered to fall into the category of optical "filters" in that they give preference to a particular wavelength to the detriment of other wavelengths. This filtering function is particularly evident when the device is used for constituting the resonator of a laser because, in this case, only the radiation having the preferred wavelength is able to oscillate to the exclusion of the others.
Toroidal resonators are also known, which comprise at least three mirrors oriented in such a way that a light beam can be reflected onto the said mirror and travel in a closed path. Generally, two progressive waves form in such resonators with oppostie propagation directions. In the laser art, the toroidal construction has in the case of a Fabry and Perot-type resonator the advantage of propagating a wave which homogeneously saturates the amplifying medium. In the following description, it is assumed that the ring has three points, or in other words the resonator is formed by three mirrors. However, it is obvious that the ring could be of a more complex nature and have for example four points located at the four corners of a rectangle. The same means can be used to make the resonators selective.